The Earth is so vast, archaeologists are still finding remnants of lost civilizations. Most recently, researchers discovered a Mayan city, hidden in the Guatemalan jungle, which is estimated to have been home to approximately 10 million citizens.

The Guardian reports that the researchers used a high-tech aerial mapping technique to find tens of thousands of hidden structures. They include Mayan houses, buildings, defense works, pyramids, an industrial-sized agricultural field and irrigation canals. At least four major Mayan ceremonial centers with plazas were also detected by the mapping technique.

News of the lost city, which was hidden in the jungle of Guatemala’s Peten region, was announced on Thursday by an alliance of US, European and Guatemalan archeologists who have been working in conjunction with Guatemala’s Mayan Heritage and Nature Foundation.

To supply the 10 million Mayan residents, massive food production would have been essential. Marcello A Canuto, a professor of anthropology at Tulane University, commented on this when he said, “That is two to three times more [inhabitants] than people were saying there were.”

The mapping technique is called Lidar, which stands for light detection and ranging. Contours hidden by dense foliage are found as the technology bounces pulsed laser light off the ground. The resulting images revealed that the Mayans altered the landscape in a drastic way. In some areas, 95 percent of the land was cultivated.

Said Francisco Estrada-Belli, a research assistant professor at Tulane University, “Their agriculture is much more intensive and therefore sustainable than we thought, and they were cultivating every inch of the land.” Estrada-Belli added that the ancient Mayas partly drained swampy road that hasn’t been farmed since.

Researchers suggest the civilization had a highly organized workforce. They predicted this based on the extensive defensive fences, ditch-and-rampart systems, and the constructed irrigation canals.

As The Guardian reports, the mapping — which revealed 810 square miles (or 2,100 square kilometers) of hidden civilization — expands the area that was intensively occupied by the Maya. The culture flourished between roughly 1,000 BC and 900 AD. Many descendants still inhabit the region.

Thomas Garrison, assistant professor of anthropology at Ithaca College in New York, used the Lidar data to look for one of the roads.

“I found it, but if I had not had the Lidar and known that that’s what it was, I would have walked right over it, because of how dense the jungle is.”

Garrison noted that the jungle grew over the abandoned Maya field and structures, rather than destroyed them. This is unlike some other ancient cities, whose fields, roads and outbuildings have been all but destroyed by the elements.

“The jungle, which has hindered us in our discovery efforts for so long, has actually worked as this great preservative tool of the impact the culture had across the landscape,” noted Garrison. The assistant professor says the finding “can’t be called anything other than a Maya fortress.”

To the researchers’ surprise, the structures were hiding in plain sight. “As soon as we saw this we all felt a little sheepish,” said Canuto, “because these were things that we had been walking over all the time.”

What else might be discovered with the Lidar technology? Only time will tell!